Nemanja Matic is a doubt for Manchester United's Premier League clash at Chelsea on Oct. 20 after being sent home from international duty with Serbia because of a back injury, sources have told ESPN FC.

Jose Mourinho faces a nervous two weeks while 11 first-team players spend time with their countries. Matic is the second player to return to the club with an injury after Luke Shaw was ruled out of England duty. The United manager cannot afford any more injury problems as he prepares for a critical six-game spell.

Mourinho, who is set to meet executive vice-chairman Ed Woodward in London this week as speculation continues about his future at Old Trafford, eased the pressure on his position by guiding United to a dramatic 3-2 win over Newcastle last Saturday.

His team will be back in action against Chelsea following the international break before games against Everton, Bournemouth and Manchester City, as well as two Champions League clashes with Italian champions Juventus.

Matic was in line to play UEFA Nations League games against Montenegro and Romania but on Tuesday returned to Manchester for assessment by medical staff at Carrington. The 30-year-old has not yet been ruled out of the trip to Stamford Bridge but faces a race against time to be passed fit to face his former club.

Meanwhile, Marouane Fellaini was absent from Belgium training on Tuesday because of a cold. He has remained with Roberto Martinez's squad and could still feature against Switzerland and Netherlands.